I. Field of the Invention
This invention relates in general to polyurethanes, chain extenders, and processes for making them. The invention relates in particular to polyamine reaction product mixtures from the reaction process of formaldehyde, an ortho monoalkylated aromatic amine and an ortho, ortho-dialkylated aromatic amine. The invention also relates to the mentioned processes as well as processes for reaction injection molding (RIM) and cast elastomer polyurethanes, including the products made therefrom especially automobile parts.
II. Description of the Prior Art
It is known to prepare useful polymers from the polyaddition reaction of isocyanates with polyols and diamines. Such polymers are made as elastomers, fibers, coatings, adhesives, as well as rigid and flexible foams.
Cast elastomers are made by carrying out the polymerization in a mold, usually at elevated temperature. Products from cast elastomer processes include tires, conveyor belts, and many other articles.
Since the development of reaction injection molding (RIM) processes in West Germany and elsewhere, polymer products have been made thereby for various purposes. These products include high density, integral skin, rigid foams as well as automobile fascia (bumpers), grills, and the like. The products are formed in seconds from positively controlled mixing heads or by other static impingement mixing means. A further description of the RIM process may be found in U.S. patent application Ser. No. 220,749, filed Dec. 29, 1980 now U.S. Pat. No. 4,314,962, which is incorporated herein by reference.
Furthermore, a reinforced RIM (RRIM) process has been developed wherein the injection materials have contained therein prior to reaction, reinforcing fibers, metals, or other shapes/materials to strengthen the resultant products. RRIM products offer a variety of uses not previously available with RIM products since the physical or other properties may be changed by the reinforcing members.
Since the reaction time to a gel state is often only about six (6) seconds, it has proven difficult to conduct RIM and RRIM processes in large molds. Often the polyurethane material hardens in a portion of the mold before the entire mold is filled despite the use of very high pressure static impingement mixing heads and other RIM equipment. Alternatively, complete mixing may not occur at fast mixing rates, resulting in poor quality products. The use of slower setting reactants has not proven entirely satisfactory since such reactants may not mix homogeneously or may otherwise result in a product without appropriate flexibility, tensile strength, hardness, or other properties.
In the past, diethyltoluene diamines and similar aromatic amines have been used, in a relatively pure form, as chain extenders in RIM, RRIM, and cast elastomer processes. Such processes are disclosed in U.S. Pat. Nos. 3,428,610 and 4,218,543. Those patents and others disclose such diamines as 2,5-diamino-xylene, 2,4-diaminomesitylene, 3,5,3'5'-tetra-ethyl-4,4-diaminodiphenylmethane, 1-methyl-3,5-diethyl-2,4-diaminobenzene, and 1,3,5-triethyl-2,4-diaminobenzene. Such chain extenders, used in pure form reliably produce products of specified characteristics in a repeatable mold time. Of course, variation of the reactant polyhydroxy or polyisocyanate will also vary the characteristics and gel/hardening times. Notably, however, the mold times are most readily regulated by the use of predetermined chain extenders.
The only notable chain extender diamine which is formed as a mixture is the mixture of 1-methyl-3,5-diethyl-2,4-diaminobenzene and 1-methyl-3,5-diethyl-2,6-diaminobenzene. This mixture is formed by ethylating the co-product 2,4-diaminotoluene and 2,6-diaminotoluene with an alkyl aluminum halide catalyst.
The diaryl diamine chain extenders are usually made by the condensation reaction of formaldehyde and an alkylated aniline. Relatively pure starting materials are used to assure consistent polyurethane-forming chain extenders.
A particular aniline will produce a methylene-bis-diphenylaniline with repeatable gel time and hardening time. For example, 2,6-diethylaniline may be condensed with formaldehyde to form methylene-bis-2,6-diethylaniline. The reaction product is about 99% bis compound and reacts in most RIM formulations with a gel time of about 7 seconds in a simple beaker gel test which is explained hereinafter.
Analogously, ortho-isopropylaniline is condensed with formaldehyde to methylene-bis-ortho-isopropylaniline of relatively good purity and gel time in the beaker gel test of about 7-8 seconds.
Finally, these chain extenders have been used in cast elastomer processes with considerably slower times, but analogously reliable results when used in pure form.